Terrorist targets may include buildings, monuments, or other fixed (or slowly-moving) structures located in urban or suburban areas. Because of their static locations in, typically, well-paved places, these fixed structures may be particularly susceptible to attacks by automobiles, trucks, buses, or other land-based vehicles. Vehicular traffic indeed is common on roadways adjacent to many of these fixed structures; should a threat vehicle exit a roadway and approach an unprotected fixed structure rapidly, it conceivably could impact the structure, or come sufficiently close to the structure to damage it via detonation of on-board explosives, before countermanding action may occur.
Accordingly, various systems have been designed to protect fixed structures from land-based vehicular attack. Guard posts with moveable barriers (“check points”) constitute one mechanism for deterring threat vehicles, for example. Other mechanisms include bollards (or other posts) positioned either in a roadway or between a roadway and an object to be protected. Existing bollards may either be embedded in the ground or in a suitable foundation or elevated from a storage position underground to a raised, above-ground position. The former bollards are frequently referred to as “passive” devices, as their positions are fixed, while the latter bollards—and other moveable barriers—are denoted “active” ones.
Another fixed-object protective system is disclosed in U.S. Patent Publication No. 2006/0018711 of Rogers, et al., published after the filing date of the provisional application to which this application claims priority. Detailed in the Rogers publication is a four-part vehicle barrier system. In a first part, roadway surfaces and traffic patterns are devised to reduce maximum travel speeds of moving vehicles. Thereafter, vehicles exiting legitimate roadways must traverse a “first impact element” (typically a curb), a deformable bed, and a “second impact element” (such as a wall) before transiting to the protected structure. In combination, these elements are intended to arrest forward motion of the vehicle.
Identified in the Rogers publication as constituting the deformable bed is compressible cellular concrete of Engineered Arresting Systems Corporation (ESCO), the assignee of this application. See Rogers ¶ 0038. Among patents issued to ESCO's predecessor-in-interest is U.S. Pat. No. 5,789,681 to Angley, et al., which describes utilizing beds of cellular concrete to decelerate vehicles including landing fixed-wing aircraft past ends of runways. Because weights and speeds of landing aircraft are high relative to those of land-based vehicles, arresting beds must be of substantial strength to slow the aircraft without damaging it. As noted in the Angley '681 patent, cellular concrete may be formulated to have adequate strength for this purpose.
Also described in the Angley '681 patent are apparatus and methods of determining compressive gradient strength (CGS) of arresting materials. For purposes of arresting runaway aircraft, materials having CGS of approximately 60/80 or 80/100 usually are used. See, e.g., U.S. Pat. No. 5,885,025 to Angley, et al., col. 4, 11. 5-10. However, such materials may not deform adequately to arrest vehicles of lesser weights.
Accordingly, ESCO developed cellular concrete of lower CGS for land-based vehicle arresting purposes. Further, because the four-part system of the Rogers publication is impractical in some situations, alternatives to these systems need be devised. Such alternative systems beneficially may inhibit vehicle incursions without need of the first and second impact elements of the Rogers publication, although either or both elements may be included if desired.